Learning Chemistry: Chemical Bond

Form 4 Chapter 5: Chemical bond
Download and find out more about the following topic.

(i) WHY DO ATOMS BOND TOGETHER?
      --> to attain stable duplet (2 electrons) or octet (8 electrons) electron arrangement

(ii) Octet rules
     --> A concept of chemical bonding theory based on the assumption that in the formation of compounds, atoms exhibit a tendency for their valence shells either to be empty or to have a full complement of eight electrons (octet).

     --> The octet rule is a simple rule of thumb that states that atoms tend to combine in such a way that they each have eight electrons in their valence shells, giving them the same electron configuration as a noble gas.

     --> The rule is applicable to the main-group elements. In simple terms, molecules or ions tend to be most stable when the outermost electron shells of their constituent atoms contain eight electrons.

(iii) Formation of ions
    --> Ion formation is the gain or loss of electrons from the outermost shell of an atom so that it form a negative or positive charge. The charge of ion is determined by the number of electrons gained or lost.

    --> Formation of positive ion. Metals atom usually have 1 - 3 electrons in the outermost shell. Metals atom can achieved the stable electron arrangement of a rare gas by losing the valence electrons. The number of electrons lost must bring the number of electron "down to" that of a prior rare gas (octet).

   --> Formation of negative ion. Non-metal atom usually have 5 - 7 electrons in the outermost shell. Non-metals atom can achieved the stable electron arrangement of a rare gas by gained of electron(s) into valence shell. The number of electrons gained must bring the number of electron "up to" that of the next rare gas (octet).

(iv) Formation of ionic bonds
--> Ionic bonds form by transferring electrons from metal atom to non-metal atom. Atoms that lose electrons become positively charged ions. Atoms that gain electrons become negatively charged ions. Oppositely charged ions attract each other and held together by strong forces of attraction. These forces act in all directions and is called ionic bond.

--> An ionic compound has a giant structure of ions.

(v) Formation of covalent bonds
--> Covalent bonds most commonly occurs when two nonmetals atoms bond together. Because both of the nonmetals will want to gain electrons, the elements involved will share electrons in an effort to fill their valence shells.

--> A good example of a covalent bond is that which occurs between two hydrogen atoms. Atoms of hydrogen (H) have one valence electron in their first electron shell. Since the capacity of this shell is two electrons, each hydrogen atom will "want" to pick up a second electron. In an effort to pick up a second electron, hydrogen atoms will react with nearby hydrogen (H) atoms to form the compound H₂. Because the hydrogen compound is a combination of equally matched atoms, the atoms will share each other's single electron, forming one covalent bond. In this way, both atoms share the stability of a full valence shell.

--> Covalent compound made up of simple molecule which are held together by weak intermolecular force of attraction.

(vi) Physical properties of ionic and covalent compounds